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Patented Mar. 8, 1 932 UNITED STATES RATENT' OFFICE f m BRADLEY, or mou'rcmm, new JERSEY, AND EDWARD r. MCKEEFE, or new I YORK, N. v, ASSIGNORS ro BRADLEY-MCKEEFE oonronarron, or NEW YORK, n. Y., 4 va oonroan'rron on NEW YORK muraoroan or woon rum, ETC.

No Drawing. Original application filed June 28, 1921, Serial No. 481,146. Divided and this application filed December 23, 1924. Serial No. 757,766,

This invention relates to improvements in the production of wood pulp from wood. This application isa division of our prior application, Serial Number 481,146, filed June i The common methods ottproducing wood pulp chemically, are the so-called soda, sulphate and sulphite processes. In the so-called soda process, the main cooking operation is dependent upon caustic soda. In the socalled sulphate process, the main cooking operation is dependent upon caustic soda assisted more or less by sodium sulphide, although some sodium carbonate and sodium sulphate may be present.

In the so-called sulphite process, the main cooking operation depends upon bisulphitcs in the presence of sulphurous acid. In the soda and sulphate processes,

accordingly, the cooking liquor is strongly alkaline, while in the sulphite process the cooking liquor is strongly acid; and it has been considered impracticable to cook wood successfully, for the production of chemical pulp, unless the cooking liquor was either strongly acid or strongly alkaline.

In all three of the processes mentioned, the cooking liquors employed act not only upon the incrusting and so-called non-cellulose .constituents or so-called lignine or lignified make the pulp difiicult to bleach with the usual bleaching materials and operations, so

that the fibres may be still further injured by the severe bleaching treatment which it is necessary to employ.

The rapidly decreasing supply of woods suitable and available for pulp making purposes and the hi h cost of equipment and operation of chemical pulp mills makes it of great national and economic importance to materially increase the yield of pul from woods which are commonly used for t e purpose, and to make available for pulp-making purposes woods ordinarily considered of little or no value for the production of high grade pulp. Furthermore, if a sufficiently high yield of suitable pulp can be obtained by an economical chemical process, the necessity for making ground wood by using a certain limited class of trees and using hydraulic power to grind such woods, is obviated, thus making available a large amount of hydraulic power for other industrial uses. The pulp obtained by chemical methods of disintegrating wood, even those now employed, is far superior in quality, including strength, to that obtained by the ground-Wood process, and a much wider range of woods can be used.

As a result of our investigations, we have been impressed with the fact that a considerable portion of the pulp content of the wood treated was not being recovered in the form of pulp, and we have therefore studied the cooking processes with a view of determining whether an increased yield of pulp could be obtained from the same amount of wood. by other chemical methods than those heretofore employed.

lVe have found that if, instead of a strongly acid or strongly alkaline cooking liquor, the cooking liquor is neutral in character or is only weakly alkaline, an increased yield of a superior ulp can be obtained. We have studied the e ect of various cooking liquors and various treatments upon different kinds of wood and have determined that the ingredients associated with the 'wood fibres may generally be considered as consisting of two kinds, namely, constituents readily removable from the fibres by a mild reagent in the presence of water at a suitable temperature and pressure, and other constituents which are less readily removable by mild reagents but which are more readily removable with strong reagents in small amount in the presence of water at a suitable temperature and pressure. In some woods and similar materials the amount of ingredients or constituents which require a strong reagent for the fibres can be removed quite readily by the use or" mild reagents while in other cases small amounts of strong reagents are advantageous in addition to the mild reagent.

Our investigations have also shown that there are greater or less differences in the various kinds of wood, but we have found that woods can be divided, generally, into three classes, namely, (1) those woods which contain little or no resinous constituents, such as poplar, birch, cottonwood, aspen, basswood and similar woods; (2) woods which contain moderate amounts of resinous constituents, such as spruce, fir, hemlock, balsam and the like; and (3) woods which contain relatively large amounts of such constituents such as Georgia pine, white pine, jack pine, longleat' pine, and other similar pines.

In general, woods of the first class contain non-fibrous constituents which are readily attacked and removed by mild rea ents either alone or with small amounts 0 strong reagents, while with woods of the second class small amounts of strong reagents in addition to the weak reagents may be advantageously employed and woods of the third class may require somewhat increased amounts of strong reagents.

Among the reagents which we consider mild reagents may be mentioned normal sodium sulphite, potassium sulphite, calcium sulphite, magnesium sulphite, sodium carbonate and potassium carbonate. Among strong reagents we include caustic soda, sodium sulphide, etc.

if wood chips are cooked under pressure with water alone, for example, at about 120 pounds per square inch saturated steam pres sure, more or. less disintegration of the wood takes place and considerable amounts of organic matter are found in the solution at the end of say four or five hours treatment at such temperature and pressure, and the solution is acid in reaction to litmus. Certain of the mild reagents which we have mentioned above will thesxselves, when used in sutlicient amount and kept distributed, maintain aneutral or slightly alkaline reaction ill. (7i"fl20l1l3 the cooking operation. Other U nts may maintain a. substantially neutral reaction with certain woods but if used in insufficient amounts may require the addition of small amounts of strong reagents to maintain the cooking liquor neutral or slightly alkaline to litmus during the cooking operation.

Among the mild reagents which we have found particularly advantageous may be mentioned normal sodium sulphite and potassium sulphite, although other can be used, including the alkaline earth metal sulphites, either alone or with regulated amounts of strong reagents, for example caustic soda. i

The amounts of reagents used in the procproduction of paper.

sulphites ess are capable of some variation. In general, however, the available base in the reagent or reagents used may be somewhat less than in the present so-called soda and sulphate processes. Cooking liquors which contain a reagent not fully soluble in the amount of liquor used should be suitably circulated so as to kee the undissolved reagent in suspension and fairly uniformly dist-ributed.

The cooking operation of the present in vention may also be carried out with less of the reagents than will completely cook the wood, and a partially cooked or undercooked wood pulp produced. For example, sodium sulphite alone can be used under conditions such that the wood is partially cooked, and the cooking operation can then be followed by a mechanical treatment to further prepare the wood pulp for subsequent treatment or use. This further mechanical treatment of the partially cooked wood may be carried out in any suitable mechanical devices or means such as are well known to those skilled in the art.

The amount of sodium sulfite required for completely cooking wood chips and giving a residual liquor which is free from acid reaction is in the neighborhood of 30% based on the air-dried weight of the wood, i. e., wood containing 10% weight of water, as explained in our prior application Serial No. 481,147, filed June 28, 1921, and with some woods a minimum of around 35% or somewhat more appears necessary. For example, in treating old poplar wood containing about 20% .of water, an amount of sodium sulfite corresponding to about 12 or 15 or even 20% of the air-dried weight of the wood did not completely cook the wood chips and give a residual liquor acid in reaction; while with about 25% of the normal sodium sulfite based on the air-dried weight of the wood the liquor was about neutral: and with 30% or more of sodium sulfite no difiiculty was had in obtaining a satisfactory pulp and in avoiding an acid reaction in the cooking liquor. In treating such poplar wood with an amount of sodium sulfite corresponding to about 12 or 15 or even 20% of the air dried weight of the wood a portion only of the non-fibrous constituents of the wood chips will be solubilized, but the amount will be sutficient to soften the chips to such an extent that individual fibers thereof may be separated from each other by mechanical treatment to yield a pulpy mass which can be employed in the The softened wood chips and pulpy mass will retain a materially greater proportion of undissolved non-cellulosic matter than is contained in conventional acid sulfite, soda or sulfate pulp derived from the same kind of wood.

Instead of carrying out the cooking operation in two successive steps or stages, with the completion of the cook during the second step or stage, the process of the present invention involves the partial or undercooking of the wood. That is, the second step or stage of the process is substituted or replaced by a mechanical treatment of the partially cooked or undercooked wood. The pulp-making operation is thus divided into steps or stages, of which one part is chemical and another part mechanical. The first part of the operation can, for example, be carried out with a mild reagent or reagents, either alone or with a strong reagent. For example, sodium sulphite alone can be used for the preliminary partial cook of the wood, and the wood can be cooked with it until it has been disintegrated to a considerable extent by the sodium sulphite liquor. This disintegration of the Wood with the sodium sulfite liquorwill solubilize non-cellulosic organic constituents thereof but the resulting softened fiber bearing material will retain a materially larger proportion of undissolved non-cellulosic organic matter than is contained in the conven- 25 tional acid sulfite, soda or sulfate pulp derived from the same kind of wood. The partially cooked wood is thereafter treated mechanically so as to further prepare the wood pulp for subsequent treatment or use. The mechanical treatment of the partially cooked wood will give a pulp containing a materially larger proportion of undissolved non-cellulosic organic matter than is contained in such conventional chemical pulps.

An advantageous method of carrying out the preliminary partial cook above described is to introduce, for example, suitable sodium sulphite cooking liquor into the digester with the wood chips, and to partially cook the wood chips with the sodium sulphite cooking liquor.

The digester can be charged with hot liquor, and the digester can be filled as full as practicable with the wood chips. The cooking liquors in this process are sufficiently inert in their action upon the valuable fibres so the chips can be cooked for different periods of time in the same charge without objectionable injury due to overcooking of part of the charge. As a result, a part of the charge can be introduced and the cooking operation commenced so that the charge can be compacted in the digester and a further amount of chips introduced so that the charge as a whole can be materially increased. For example, the wood chips and the cooking liquor may be run into the digester simultaneously and the liquor circulated. for example, by a steam jet, thus packing the chips more closely and removing some of the contained air, etc. so that a considerably increased amount of wood chips can be introduced into the di rester in a single charge, without objectionable overcooking of the part of the charge first introduced.

When the partial cooking of the wood is carried out with a sodium sulphitecooking liquor, the liquor may be withdrawn at the end of the partial cook. For example, resinous pine woods can be cooked at a temperature corresponding to about 120 pounds saturated steam pressure for about 4 or 5 hours, or for a lesser time, with a solution containing sodium sulphite, and the residual liquor can then be removed from the chips. Such a partial cook will result in solubilizing a sufiicient portion of the non-cellulosic organic constituents of the wood. that are normally insoluble in water, to render individual fibers thereof separable from each other by mechanical distintegrating treatment of the softened material; but the solubilizing treatment will leave the softened :iber bearing material in a condition such that it retains a materially larger proportion of undissolved non-cel lulosic organic matter than is contained in conventional acid sulfite, soda or sulfate pulp derived from the same wood. 7

It is one advantage of the present invention that indirect heating of the digester can be employed in an advantageous manner, in asmuch as the cooking liquor may be either neutral or mildly alkaline to litmus, and thus have less objectionable corroding action than results from the use of acid liquors. The residual liquors produced, as well as the cooking liquors during the cooking operation have less organic matter in solution than the liquors of the usual pulp processes, if the same amount of liquor is employed, and the organic matter'partakes of a somewhat different character and is less liable to deposit on the tubes or coils of a heater or heat exchanger.

We have also found that it is not necessary to keep the chips submerged during the cook ingoperations, provided the chips are properly subjected to the action of the cooking liquor by employing suitable circulation, for

example, by spreading the cooking liquor at the top of the digester and allowing it to penetrate down around or through the chips to be again returned to the top and recirculated. This method of procedure permits the employment of a lesser quantity of cooking liquor,- with saving in the amount of liquor to be pumped and in the heat required for heating the body of liquor, as well as in evaporation and other recovery steps owing to the lesser amount of residual liquor to handle. By asuitable arrangement of supply tanks and connections, the composition of i the cooking, liquor to be circulated can be varied by introducing additional liquor of a different character, so that it will be introduced into the digester along with the other liquor that is being-circulated. When the cooking operation has reached a desired point, for example, the liquor can be Withdrawn. The liquor used in one cooking operation or in a preliminary portion of the cook may even be drawn off and circulated through another digester, thus further carrying out the selective treatment of different charges of chips in different digesters, orutilizing the same liquor for treating successive charges in different digestersL The liquor drawn off from the digester after the partial cook is an advantageous liquor for use in the treatment of additional wood thus enabling the chemical constituents containedin the liquor including unconsumed chemicals, and prodnets of the first solubilizing treatment to be utilized in a subsequent softening and solu bilizing treatment. T

It will accordingly be seen and understood that the present invention provides a process of producing wood pulp from wood in which a neutral or weakly alkaline cooking liquor 1 may be used and that the cookin operation is carried out with incomplete coo ring of the v wood, so that a partially cooked or undercooked material is produced; and that this partial cooking operation is followed by a suitable mechanical treatment to further prepare the material for subsequent treatment or use. It will also be seen that the preliminary or partial cooking of the wood may be carried out with less of the reagents than will completely cook the wood, with resulting economy in the amount of reagents required. It will also be seen that the chemical treatment of the wood will nevertheless soften the original wood structure, and dissolve away therefrom a part of the non-fibrous constituents so that suitable pulp can be prozs' duced from the partially treated or undercooked wood, by suitable mechanical treatment. This gives a new pulp product which is generally superior to ordinary mechanical pulp obtained from the same wood by the a customary ground-wood process. For ex ample, in the case of pulp made by mechanical treatment following the partial cooking of wood with a solution which contains a sulphite of sodium, the pulp will have had rea moved therefrom a part of the non-fibrous constituents, while the constituents which have not been removed by the partial chemical treatment and by the subsequent washing, will remain with the product of the subsequent mechanical treatment which further prepares the wood pulp for subsequent treatment or use.

The present invention accordingly ma provide approximately or substantially the 65 maximum yield of pulp and presents many other advantages,such as those hereinbefore pointed out.

We claim: 1. The process of producing pulp, which includes subjecting wood to a softening treatment comprising the step of solubilizing a portion only of the non-cellulosic organic constituents thereof, that are normally insoluble in water, by means'of non-acid material containing a sulfite, discontinuing such solubilizing step while the softened fiber bearing material retains a materially larger proportion of undissolved non-cellulosic organic matter than is contained in conventional acid sulfite, soda or sulfate pulp derived from the same kind of wood, and subjecting the fiber bearing material to a mechanical disintegrating treatment whereby to obtain pulp suitable for use in manufacturing a paper or pulp product, such pulp,

containing a materially larger proportion of undissolved non-cellulosic organic matter than is contained in conventional chemical pulp derived from the same kind of wood by either acid sulfite, soda or sulfate processes. 2. The process of producing pulp, which includes subjecting Wood to a softening 'terial to a mechanical disintegrating treatment whereby to obtain pulpsuitable for use in manufacturing a paper or pulp product, such pulp containing a materiallylarger pro portion of undissolved non-cellulosic organic matter than is contained in conventional chemical pulp derived from the same kind of wood by either acid sulfite, soda or sulfate processes.

3. The process of producing pulp, which includes subjecting wood to a softening treatment comprisin the step of solubilizing a portion only of the non-cellulosic organic constituents thereof, that are normally insoluble in water, by means of a normal sulfite, discontinuing such solubilizing step while the softened fiber bearing material retains a materially larger proportion of undissolved non-cellulosic organic matter than is contained in conventional acid sulfite, soda or sulfate pulp derived from the same kind of wood, and subjecting the fiber bearing material to a mechanical disintegratingtreatment whereby to obtain pulp suitable for use in manufacturing a paper or pulp product,

such pulp containing a materially larger proportion of undissolved non-cellulosic organic matter than is contained in conventional chemical pulp derived from the same kind of wood by either acid sulfite, soda or sulfate processes.

4;. The process of producing pulp, which includes subjecting wood to a softening treatment comprising the step of solubilizing a portion only of the non-cellulosic organic constituents thereof, that are normally insoluble in water, by means of substantially neutral mildl alkaline material, discontinuing such solu ilizing step while the softened fiber bearing material retains a materially larger proportion of undissolved non-cellulosic organic matter than is contained in conventional acid sulfite, soda or sulfate pulp derived from the same kind of wood and subjecting the fiber bearing material to a mechanical disintegratin treatment whereby m to obtain pulp suitable lor use in manufacturing a paper or pulp product, such pulp containing a materially larger proportion of undissolved non-cellulosic organic matter than is contained in conventional chemical pulp derived from the same kind of wood by either acid sulfite, soda or sulfate processes.

5. A further im rovement in the process of claim 1 characterized by the use, in the solubilizing step set forth therein, of a cooking liquor that is non-acid to litmus and contains a normal alkali sulfite but is free from alkali hydroxide and alkali sulfid.

6. A further improvement in the process 25 of claim 2 characterized b the use, in the solubilizing step set forth t erein, of a cooking liquor that is non-acid to litmus and contains a normal sulfite of an alkali metal but iisdfree from alkali hydroxide and alkali sul- 80 7. A further improvement in the process of claim 4 characterized by the use, in the solu- ,bilizing step set forth therein, of a cooking lifiuid that is substantially neutral or mildl 3 iai aline to litmus and contains a normal su te. r

In testimony whereof we aifix our signatures.

LINN BRADLEY. m EDWARD P. MGKEEFE. 

